1. Field of the Invention
The present invention relates to a rotating electrical machine having a permanent magnet for supplying magnetic flux to an armature core in cooperation with a field winding in a rotor.
2. Description of the Related Art
For example, in a charging generator (alternator) for a vehicle, in order to increase an electrical load necessary for the vehicle or improve fuel consumption due to a light weight, a high output, a small size, and a light weight are required. In order to address such requirements, by adding a magnetizing force due to a permanent magnet to the magnetic field of the generator, leakage magnetic flux between magnetic poles is reduced and efficient magnetic flux increases to improve an output. However, in the generator having such a configuration, even if electrical generation is performed only by the magnetic flux of the permanent magnet without flowing field current, generated electrical energy exceeds the electrical load at the time of a small electrical load and high rotation and thus a battery may be damaged due to overcharging or an abnormal voltage may be applied to the electrical load to be damaged.
Japanese Patent 3063106 discloses a generator including a permanent magnetic and a field winding in a magnetic field, in which magnetic flux passing through an armature core, that is, linked to an armature coil, increases or decreases by changing a value of field current flowing in a field winding and a flow direction thereof such that an output voltage is adjusted to an adequate value to prevent an over-voltage from being generated.
However, in the technology disclosed in Japanese Patent 3063106, a rotor includes two kinds of rotors, that is, a first rotor including at least the field winding and a second rotor including the permanent magnet. Thus, the structure thereof is complicated and weight or cost increases. In addition, since a switching means for switching the flow direction of the field current is further included, the cost more increases.
Furthermore, when the rotor rotates at a high speed and an electrical load is small, in order to suppress the over-voltage from being generated, there is a problem that the current must continuously flow in the field winding in a direction for reducing the magnetic flux of the permanent magnet and thus power consumption increases.